1. Field of the Invention
The present invention relates to an improved expandable muff mould comprising an annular elastic metal member which is provided with an axial slot and a wedge means adapted to be detachably affixed in the slot, the muff mould expanding to a larger inner diameter with the wedge means inserted in the slot than with the wedge means removed therefrom.
The muff mould according to the invention finds particular application in connection with the forming of a cylindrical socket portion on a plastic pipe, the socket being formed by winding a web soaked in curable plastic material around the end portion of the pipe and the mould which has been inserted therewithin.
2. Statement of the Prior Art
In German DE-OS 23 44 715 there is disclosed a ring-shaped core used for the production of a cylindrical socket or transition portions on moulded plastic articles. The ring-shaped core is made from a single elastic blank and is provided with an axial slot. A sealing element can be inserted into the slot, the size of the element determining the degree of expansion of the core. According to this German Auslegeschrift, the core is made from steel and the sealing element from rubber. Further, this publication suggests the holding of the element in the core slot by screw connections.
The handling of this core when preparing it for a moulding operation is both cumbersome and time-consuming, and the rubber sealing element is apt to yield when a web soaked in a curable plastic is wound around the core, the yielding of the rubber element sacrificing the accuracy of the finished plastic product.
From U.S. Pat. No. 2,105,047 there is known a stretcher for uniform cap covers comprising two segmental shells of nearly semi-circular shape. The two shells are kept together by two intermediate link mechanisms each of which is formed from stiff wire bent to a suitable shape to effect a separation of the two shells and consequent effective stretching of a cap cover engaged on the shells.
A stretcher like this is not suitable for the field of application contemplated in connection with the present invention, the known stretcher not being made from a single elastic blank nor having a wedge means which in locked position is flush with the outer surface of the mould.